The influence of the electronic specific heat on swift heavy ion irradiation simulations of silicon

Abstract

Abstract. Swift heavy ion (SHI) irradiation of materials is often modelled using the two-temperature model. While the model has been successful in describing SHI damage in metals, it fails to account for the presence of a bandgap in semiconductors and insulators. Here we explore the potential to overcome this limitation by explicitly incorporating the influence of the bandgap in the parameterisation of the electronic specific heat for Si. The specific heat as a function of electronic temperature is calculated using finite temperature density functional theory with three different exchange correlation functionals, each with a characteristic bandgap. These electronic temperature dependent specific heats are employed with two temperature molecular dynamics to model ion track creation in Si. The results obtained using a specific heat derived from density functional theory showed dramatically reduced defect creation compared to models that used the free electron gas specific heat. As a consequence, the track radii are smaller and in much better agreement with experimental observations. We also observe a correlation between the width of the band gap and the track radius, arising due to the variation in the temperature dependence of the electronic specific heat.

Femtosecond Laser-Induced Thermal Transport in Silicon with Liquid Cooling Bath

“…The thermal conductivity of the lattice is chosen to be λ l = 130 W/mK for simplicity in this calculation. The specific heat of the electron depends on the electron temperature, and we use a linear relation C e = γ T e , where γ = 50 J/m 3 K 2 [41]. We assume electron thermal conductivity in silicon follows the Wiedemann-Franz law, λ e = Lσ T e , where Lσ = 24.4 µW/mK 2 [42].…”

“…We assume electron thermal conductivity in silicon follows the Wiedemann-Franz law, λ e = Lσ T e , where Lσ = 24.4 µW/mK 2 [42]. Following the methodology in Khara et al, the lattice-electron coupling term is calculated to be G = 2.8 × 10 17 W/m 3 K [41]. The solid-liquid coupling coefficient is chosen W = 10 8 W/m 2 K as the description following Equation (9).…”

Simulating electronically driven structural changes in silicon with two-temperature molecular dynamics

“…Silicon is a widely studied material in the context of strongly driven phase transitions, both experimentally [1][2][3][4][5][6] and theoretically [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], where it is found to melt on a subpicosecond timescale at high excitations. Most theoretical studies of nonthermal melting in silicon have employed ab initio simulation methods.…”

Modelling radiation effects in solids with two-temperature molecular dynamics

“…In these materials is zero at low because there is insufficient thermal energy to excite electrons across the gap. As is very sensitive to the size of the bandgap, it is necessary to employ a DFT functional that correctly reproduces this feature, as it has been demonstrated that different functionals produce very different degrees of damage in SHI simulations of silicon [37]. Calculating the dependence of for band gap materials is more challenging as ( )is zero in these materials so equation 3.1 diverges.…”

“…The model was coupled to MD to give an extended version of 2T-MD and used to model SHI irradiation in Ge [68]. As argued above, however, the use of the electron density as an additional parameter is unnecessary, and other studies of SHI irradiation in Si [37], UO2 [69] and SiO2 [70] have omitted it.…”